My present invention relates to an apparatus for the stacking and delivery of plastic bags, especially bags for use in automatic filling or packaging machines and, more particularly, to an apparatus wherein one or more bags and preferably a stack of bags are delivered by a movable stack chain and at the discharge station a robot with a gripping hand is engageable with the stack to remove it from the chain or conveyor.
The use of a robot to remove stacks of bags from an endless conveyor is disclosed in general terms in DE 38 34 115 C1. The device described in this patent requires the connection of the bags of the stack with a wire stirrup and the removal of the stack mounted on the stirrup or connected by the stirrup, utilizing the robot. The robot and its construction and operation is not described in detail, although the patent does recognize that robots utilized for handling stacks of bags are generally complex and expensive.
In DE 198 479 32, corresponding to copending U.S. application Ser. No. 09/535,713 filed Mar. 27, 2000 (U.S. Pat. No. 6,315,516 issued Nov. 13, 2001), the use of a robot for the removal and transfer of bag stacks is also described. In this case, stacks of plastic bags having bottom folds are collected upon pins which pass through openings previously formed in the bags. At a discharge station, the stacks are removed from the bag for packaging. The operation is automated and the improvement described in that application serves to simplify and accelerate the transfer of the stack.
To enable the bags to be mounted on the pins, the bags are preformed with relatively large hanging openings and the stacking pins are provided in pairs to allow the bags to be suspended on the pins and collected in stacks, utilizing these is openings. The bags and the stacks formed on the pins hang freely from the latter. The stacks can be fused or joined into pads or collections of the bags for packaging.
It is the principal object of the present invention to provide an improved apparatus which can serve for the delivery of plastic bags or stacks of plastic bags, especially plastic bags for use in automatic packaging machinery, whereby the removal of the bags or stacks from the stacking device is facilitated and the bags or their stacks can be transferred at a delivery station without difficulty.
It is also an object of this invention to provide an improved transport and delivery apparatus which eliminates the need to provide large openings in a bag for suspension of the bag from the stack conveyor and nevertheless ensure effective and reliable delivery of the bags or stacks thereof.
Still another object of this invention is to provide an apparatus for delivering plastic bags, e.g. as stacks, whereby drawbacks of earlier systems are eliminated.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, by providing, as the stacking elements of the conveyor, needles piercing through the plastic bags while the robot hand or grip is provided with stripping means cooperating with the needles. Because of the configuration of the stacking elements as needles, it is no longer necessary to form the plastic bags with relatively large, stamped out suspension holes. While the plastic film material of the bag grips the needles tightly and lies adjacent the needles, the invention provides that any problem because the bags hug the needles can be obviated by providing the gripper or gripping hand with stripper means cooperating with the needles for overcoming any retention force between the needles and the bags.
The stripping means provided for this purpose can be comparatively simple and can comprise a support element and a holding element movably mounted relative to the support element. The support element can have a shank or arm which engages beneath the plastic bag or the stack of plastic bags and preferably an upper shank which is parallel to that lower shank but is spaced therefrom.
Between the two shanks a stripper element with a holding element is provided which can be displaced on a piston rod of a piston and cylinder unit to which those elements can be attached so that the elements are displaced by the piston and cylinder units. The device, namely, the gripping hand, can be so configured that it closely surrounds the needle and encompasses the needle through at least 180xc2x0 and provides during the clamping and withdrawal operations a retraction function.
According to one aspect of the invention, the apparatus for stacking and transporting or delivering plastic bags, especially plastic bags for automatic packaging machines, comprises a stacking chain which is cyclically movable and has stacking elements forming a conveyor therewith and cooperating with the robot at the delivery station. The robot has a gripper hand with a tongs-like gripping action. The stacking elements of the conveyor are formed as needles and the gripping hand is provided with a stripper facility cooperating with the needles.
The stripper facility can comprise a support element and a holding element movable relative thereto. The support element has a shank which engages below the end of the bag or stack of bags pierced by the needles and, possibly, an upper shank parallel to that lower shank, both of which extend inwardly on the gripper hand. The two shanks and the support element in cross section can form a substantially U-shaped transverse beam or bar. The upper shank can carry the piston and cylinder unit previously mentioned which can be so constructed and arranged as to prevent rotation of the piston rod or the elements thereon. The holding element affixed to the piston rod can have a z-shape and can engage around the needle through at least 180xc2x0. The holding element can have one part of the Z which is affixed to the piston rod of the piston and cylinder unit and another part of the z parallel to the first part and which is formed with a longitudinal slit opening toward the needle.